Segment Information (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Restructuring and other charges	$ 1.4	$ 2.4
Operating income	27.8	20.3
Depreciation, Depletion and Amortization	14.7	14.0
Payments to Acquire Productive Assets	15.6	15.2
Net sales	237.4	212.6
Mueller Co. [Member]
Segment Reporting Information [Line Items]
Restructuring and other charges	0.1	0.0
Operating income	41.6	35.5
Depreciation, Depletion and Amortization	12.5	12.0
Payments to Acquire Productive Assets	14.7	14.5
Net sales	215.9	192.3
Mueller Co. [Member] | Central Region [Member]
Segment Reporting Information [Line Items]
Net sales	56.9	46.4
Corporate
Segment Reporting Information [Line Items]
Restructuring and other charges	1.3	2.4
Operating income	(12.3)	(13.4)
Depreciation, Depletion and Amortization	0.1	0.0
Payments to Acquire Productive Assets	0.1	0.1
Mueller Technologies [Member]
Segment Reporting Information [Line Items]
Restructuring and other charges	0.0	0.0
Operating income	(1.5)	(1.8)
Depreciation, Depletion and Amortization	2.1	2.0
Payments to Acquire Productive Assets	0.8	0.6
Net sales	21.5	20.3
Mueller Technologies [Member] | Central Region [Member]
Segment Reporting Information [Line Items]
Net sales	$ 4.9	$ 4.8